This invention relates to tubing expansion, and in particular to an expansion tool and method for expanding tubing downhole.
The oil and gas exploration and production industry is making increasing use of expandable tubing for use as, for example, casing and liner, in straddles, and as a support for expandable sand screens. The tubing may be slotted, such as the tubing and sand screens sold under the EST and ESS trade marks by the applicant, or may have a solid wall. Various forms of expansion tools have been utilised, including expansion cones and mandrels which are pushed or pulled through tubing by mechanical or hydraulic forces. However, these methods typically require transfer of significant forces from surface, and furthermore there are difficulties associated with use of hydraulic forces in the expansion of slotted tubing; the presence of the slots in the unexpanded tubing prevents the use of hydraulic force to drive the cone or mandrel through the tube. A number of the difficulties associated with expansion cones and mandrels may be avoided by use of rotary expansion tools, which feature radially extending rollers which are urged outwardly into rolling contact with the tubing to be expanded while the tool is rotated and advanced through the tubing. However, it has been found that the torques induced by such rotating tools may induce twisting in the expandable tubing, particularly in slotted tubing.
It is among the objectives of embodiments of the present invention to provide an expansion method and apparatus which obviates or mitigates these difficulties.
According to one aspect of the present invention there is provided a method of expanding tubing, the method comprising the steps:
providing a length of expandable tubing of a first diameter;
locating an expansion tool in the tubing;
applying a plurality of impulses to the tool to drive the tool through the tubing and expand the tubing to a larger second diameter.
According to a further aspect of the present invention there is provided tubing expansion apparatus comprising:
an expansion tool for advancement through a length of expandable tubing to expand the tubing from a smaller first diameter to a larger second diameter; and
means for transmitting a tubing-expanding impulse to the tool.
Preferably, the expansion operation is carried out downhole.
The impulses may be provided by any appropriate means and thus the invention provides a flexibility in the range of apparatus and supports that may be utilised to expand tubing downhole. The impulses may be produced hydraulically, for example by pumping fluid through a valve or other variable flow restriction, such that the variation in flow through the restriction induces a variation in fluid pressure. The resulting varying fluid pressure may act directly on the expansion tool, or indirectly via a shock sub or the like. One embodiment of the invention may involve the combination of a conventional hydraulic hammer with an expansion cone provided with an anvil or other arrangement for cooperating with the hammer, possibly also in combination with an appropriate number of weight subs. Alternatively, or in addition, a reciprocating or otherwise movable mass may be utilised, the mass reciprocating in response to a controlled varying flow of hydraulic fluid, and impacting on the expansion tool, typically via an anvil. It is preferred that the impulse force is created adjacent the expansion tool, to limit attenuation. As such arrangements would not require a fluid seal between the expansion tool, typically in the form of an expansion cone, and the tubing, these embodiments of the invention permit expansion of slotted tubing by means of hydraulically-actuated apparatus. Furthermore, the use of hydraulic pressure to induce or create impulses or impacts will tend to allow expansion of tubing utilising lower pressures than are required to drive an expansion cone through tubing using conventional methods; the apparatus utilised may therefore be rated for operation at lower pressures, and be less complex and expensive.
Other embodiments may utilise mechanical actuation, for example a rotating shaft may be linked to the expansion tool via an appropriate cam profile. In a preferred embodiment, a rotating shaft is coupled to a reciprocating mass via a cam arrangement, such that rotation of the shaft causes the mass to impact on the expansion tool. The mass may be spring-mounted, the spring tending to bias the mass towards the tool. The mass may be restrained against rotation relative to the shaft, and may be splined or otherwise coupled to the tool. Rotation of the shaft may be achieved by any appropriate means, for example from a top drive or kelly drive on surface, by a positive displacement motor (PDM) or other form of downhole hydraulic motor, or by a downhole electric motor.
Alternatively, electrical or magnetic actuation may be utilised, for example a magnetic pulsing field may be produced to induce reciprocal movement of a magnetic mass which impacts on the expansion tool, or a piezo-ceramic stack or magneto-strictive materials may be provided which expand or contract in response to applied electrical potentials.
As the expansion tool is not simply being pushed or pulled through the tubing by a substantially constant elevated force applied via the tool support, the tool support may not necessarily have to be capable of transmitting a compression or tension force of similar order to the force applied to the tool to achieve expansion. This facilitates use of lighter, reelable supports, such as coil tubing, and may permit use of a downhole tractor to advance the expansion tool through the tubing.
The expansion tool may be provided in combination with a further expansion tool, and in particular a further expansion tool which utilises a different expansion mechanism. In one embodiment, a rolling element expansion tool may be provided above an expansion cone to which impulses or impacts are applied, the leading expansion cone providing an initial degree of expansion and the following rolling element expansion tool providing a further degree of expansion. If the rolling element expansion tool is provided with one or more radially movable rolling elements, such an arrangement offers the advantage that the expansion tools are easier to pull back out; the tubing will have been expanded to a larger diameter than the normally fixed diameter expansion cone.
Where the expansion tool is in the form of an expansion cone, the cone angle may be selected such that advancement of the cone through the tubing is retained. Where the cone angle is steeper, the tendency for the tubing to elastically contract between impacts may be sufficient to overcome any residual applied force or weight, and the friction between the cone and the tubing, thus pushing the cone back. However, such difficulties may be overcome by appropriate selection of cone angle or by application of weight or provision of a ratchet or slip arrangement.
The impulses are preferably applied to the expansion tool with a frequency of at least one cycle per second, and most preferably with a frequency between 10 and 50 Hz. If desired or appropriate higher frequencies may be utilised, and indeed in certain applications ultrasonic frequencies may be appropriate.
In existing downhole applications, where any significant length of tubing is to be expanded, it is convenient for the expansion tool to advance through the bore at a rate of approximately 10 feet (3 meters) per minute. For this rate of advancement, the frequency of the impulses or impacts applied to the tool are preferably in the region of 20 Hz, as this equates to a distance of travel of the tool of around 2.5 mm per impact. For any significantly slower frequencies, the travel of the tool per impact required to obtain the preferred rate of advancement becomes difficult to achieve.
The apparatus preferably defines a throughbore to permit fluid communication through the apparatus, and to permit tools and devices, such as fishing tools or cement plugs, to be passed through the apparatus.
In embodiments of the invention utilised to expand solid-walled or otherwise fluid-tight tubing, the impulse expansion mechanism may be assisted by applying elevated fluid pressure to the interior of the tubing in the region of the expansion tool, as described in our co-pending PCT patent application PCT/GB01/04958, the disclosure of which is incorporated herein by reference. In such embodiments, the fluid pressure force may provide a tubing expansion force approaching the yield strength of the tubing, such that the additional expansion force supplied by the expansion tool and necessary to induce yield and allow expansion of the tubing is relatively low. The elevated pressure may be present at a substantially constant level, or may be provided in the form of pulses, timed to coincide with the impulses to the expansion tool.
According to a still further aspect of the present invention there is provided tubing expansion apparatus, the apparatus comprising:
an expansion device for advancement through a length of expandable tubing to expand the tubing from a smaller first diameter to a larger second diameter, the device being adapted to cycle between a smaller diameter first configuration and a larger diameter second configuration;
means for cycling the device between said configurations; and
means for advancing the cycling means through the tubing.
The device may comprise a hollow flexible body, the dimensions of the body being variable in response to variations in internal fluid pressure. Preferably, the body is elastomeric. The body may carry rigid members for contact with an internal surface of the tubing.
According to a yet further aspect of the present invention there is provided a method of expanding tubing, the method comprising: providing a length of expandable tubing of a first diameter;
locating an expansion device in the tubing;
cycling the expansion device between a smaller diameter first configuration and a larger diameter second configuration using a cycling device, in said second configuration the expansion device describing a greater diameter than said tubing first diameter such that the tubing is expanded to a greater second diameter; and
advancing the cycling device through the tubing.
Preferably, the device is cycled at least once a second.